Estimating Vp/Vs ratios using smooth dynamic image warping

Abstract

Interval Vp/Vs ratios can be estimated from derivatives of vertical shifts that align reflections in PP and PS images. This alignment, however, is nontrivial because features in PS images are not simply time-shifted versions of features in PP images. To align PP and PS images we use a smooth dynamic image warping algorithm that can be accurate with respect to problems unrelated to time shifts, such as differences in noise and reflection waveforms. To optimize accuracy of estimated time shifts and Vp/Vs ratios, we automatically construct a coarse lattice of points located on reflections with high amplitudes, and then estimate time shifts at only those points. By adjusting the coarseness of the lattice, we trade off resolution of changes in Vp/Vs with increased accuracy in Vp/Vs estimates. By processing 3D PP and PS images we learned that our estimates of Vp/Vs cannot be obtained by simply smoothing estimates obtained using other methods.